Germany provides a context in which materialism within the Roman Catholic church is offensively evident. Some of the principalities, which together make up the Holy Roman empire, are ruled by unscrupulous prelates living in the style of Renaissance princes. Foremost among them is Albert, archbishop of Mainz and one of the seven imperial electors.

By the age of twenty-four Albert holds a bishopric and a second archbishopric in addition to Mainz. Such plurality is against canon law. But the pope, Leo X, agrees to overlook the irregularity in return for a large donation to the building costs of the new St Peter's.

Both pope and archbishop are men of the world (the pope is a Medici). Leo makes it possible for Albert to recover his costs by granting him the concession for the sale of indulgences towards the building of St Peter's. Half the money for each indulgence is go to Rome; the other half will help to pay off Albert's debts (he has borrowed the money for the original donation from the Fuggers of Augsburg).

This secret arrangement might distress the faithful if they knew of it. But more immediately shocking to some is the behaviour of the friar Johann Tetzel, whom Albert employs to sell the indulgences.

Tetzel is a showman. When preaching to gullible crowds in German towns he goes far beyond the official doctrine of indulgences. He promises the immediate release of loved ones from the pain of Purgatory as soon as a purchase is made. He even has a catchy jingle to make the point: 'As soon as the coin in the coffer rings, The soul from Purgatory springs.'

In October 1517 some parishioners return to Wittenberg with indulgences which they have bought from Tetzel - indulgences so powerful, some have been led to believe, that they could pardon a man who had raped the Virgin Mary. News of this travesty reaches the ears of a professor at the university of Wittenberg.

Luther's ninety-five theses: 1517

Martin Luther, a man both solemn and passionate, is an Augustinian friar teaching theology at the university recently founded in Wittenberg by Frederick the Wise, the elector of Saxony. Obsessed by his own unworthiness, he comes to the conclusion that no amount of virtue or good behaviour can be the basis of salvation (as proposed in the doctrine known as justification by works). If the Christian life is not to be meaningless, he argues, a sinner's faith must be the only merit for which God's grace might be granted.

Luther therefore becomes a passionate believer in an alternative doctrine, justification by faith, for which he finds evidence in the writings of St Paul.

Nothing could be further from the concept of justification by faith than Tetzel's impudent selling of God's grace. Luther has often argued against the sale of indulgences in his sermons. Now he takes a more public stand. He writes out ninety-five propositions about the nature of faith and contemporary church practice.

The tone of these 'theses', as they come to be known, is academic. But the underlying gist, apart from overt criticism of indulgences, is that truth is to be sought in scripture rather than in the teaching of the church. By nailing his theses to the door of All Saints' in Wittenberg, as Luther does on 31 October 1517, he is merely proposing them as subjects for debate.

Instead of launching a debate in Wittenberg, the ninety-five theses spark off a European conflagration of unparalleled violence. The Reformation ravages western Christendom for more than a century, bringing violent intolerance and hatred which lasts in some Christian communities down to the present day. No sectarian dispute in any other religion has matched the destructive force, the brutality and the bitterness which begins in Wittenberg in 1517.

Luther is as surprised as anyone else by the eruption which now engulfs him - slowly at first but with accelerating pace after a year or two. Its violence derives from several unusual elements.

The papacy is determined to suppress this impertinence. Luther's writings are burnt in Rome in 1520; his excommunication follows in 1521. This is the predictable part. The unexpected elements are the groundswell of support in Germany, nourished by a deep resentment of papal interference; and the effect of the relatively new craft of printing.

Before Gutenberg, news of Luther's heresy would have circulated only slowly. But now copies of the ninety-five theses are all over Europe within weeks. A fierce debate develops, with pamphlets pouring from the presses - many of them from Luther's pen. Within six years, by 1523, Europe's printers produce 1300 different editions of his tracts.

In these circumstances it is impossible for the issue to be swept under the carpet. Any action taken against Luther in person is certain to provoke a crisis - though in the early years his safety depends heavily on the protection of Frederick the Wise, proud of his university and reluctant to hand over to Rome its famous theologian, however controversial.

Support for the excommunicated monk is so strong among German knights that the young emperor, Charles V, is prevailed upon to hear his case at a diet held in 1521 in Worms. Luther is given a safe conduct for his journey to and from the diet. He is no doubt aware of the value of an imperial safe conduct to John Huss a century earlier, but he accepts the challenge.

The Diet of Worms: 1521

Where Huss had slipped into Constance in 1414 almost alone, Luther arrives at the diet at Worms supported by a large number of enthusiastic German knights. Nevertheless the purpose of the confrontation, from the emperor's point of view, is a demand that he should recant.

In a lengthy speech Luther explains that he will recant any of his views if they can be proved wrong by scripture or reason. Otherwise he must remain true to his conscience and to his understanding of God's word. The presses soon reduce this to the pithy statement which has been remembered ever since: Hier stehe ich. Ich kann nicht anders., 'Here I stand. I can not do otherwise.'

Luther's stand leads, eventually, to the emergence of the first sect to break away from the Roman Catholic church and to survive the opposition of the papacy - Lutheranism, finally established by the Peace of Augsburg in 1555. This first Protestant faith is soon followed by others, violently disagreeing among themselves. Zwingli goes further than Luther. The Anabaptists far outstrip either. Meanwhile Henry VIII devises a new English church for personal purposes.

The papacy, unable to stem the tide, calls the council of Trent and develops the Catholic Reformation - Rome's own rigorously virtuous programme of reform.

Zwingli: 1518-1525

The towns of Switzerland are the perfect context for the new movement of reform. Independent, free of any feudal ties, they are run by councils in which the merchants of the guilds usually have the predominant voice. The largest town is Zürich, where from 1518 there is a powerful preacher on the cathedral staff - Huldreich Zwingli.

Zwingli's first overt gesture against Catholic dogma is his eating of sausage during Lent in 1522, an event usually taken as the start of the Swiss Reformation. Zwingli, experiencing little of the opposition faced by Luther in Germany, persuades Zürich to accept sweeping Protestant reforms. But, like Luther in Wittenberg, he is soon confronted by reformers more radical than himself.

Anabaptists: 1525

Zürich, swift in its acceptance of Zwingli's Protestant logic, is also the first city where radical reformers insist upon logic in a ritual central to the Christian faith - that of baptism (one of only two Sacraments retained by Luther and Zwingli, the other being the Eucharist).

If each Christian in the reformed faith is to be personally responsible for his or her relationship with God, how can a mewling infant be offered the sacrament of baptism? In the gospels, there is only an adult baptism - that of Jesus himself. In the early years of the religion most Christians were converts, choosing the faith and receiving baptism as adults.

Arguments for adult baptism formed part of the unrest in Wittenberg during Luther's absence in 1521. Now, in 1525 in Zürich, Conrad Grebel - a young follower of Zwingli - takes a drastic step. He baptises a former Catholic priest, Georg Blaurock.

The action forms part of a wider programme, derived by Grebel from the gospels. His tenets include a free church of believers, fully detached from the state; refusal to swear an oath; and pacifism. The last two commitments, subsequently of great importance to all radical sects in this tradition, derive from Christ's sermon on the mount (Matthew, v, 33-48).

Grebel's act of baptism is a direct challenge to his former mentor, Zwingli, who is closely associated with the state - indeed he has a guaranteed majority of supporters on Zürich's city council. It can also be seen as blasphemy, since this is a rebaptism. It denies the validity of a sacrament, in the form of Georg Blaurock's original baptism as an infant.

The reaction of Zürich, under Zwingli's guidance, is swift and extreme. Anyone even attending a ceremony of this kind is to be liable to death by drowning - if they want water they shall have it. It is the start of a long ordeal of persecution for Anabaptists (from Greek for 'baptize again'). No other Christian sect has had such a high proportion of martyrs.

Swiss reform: 1525-1531

Zürich is intolerant of the radical programme of the Anabaptists, but nevertheless this is the city in which the pattern of a fully reformed church is first established. The central detail, on which Zwingli goes much further than Luther, is the nature of the Eucharist.

By 1525 Zwingli has already replaced the mass (containing implications of a sacrificial ritual) with a simple service in which the altar becomes a communion table. In Zwingli's communion the bread and the wine, both of which are given to the congregation, merely symbolize Christ's body and blood. Luther maintains a more traditional view. The two men clash dramatically at Marburg, in 1529. They fail to reach agreement.

In this respect the Swiss reform differs intrinsically from the Lutheran version (or, later, the Anglican variety). It does so also on the issue of holy images. It is only the Swiss example which causes sculpture and painting to be smashed in many churches of Europe during the 16th century.

The independence of each Swiss canton has enabled Zürich to effect very rapidly its own programme of reform. But the same political freedom also makes it impossible for the whole federation to move together into reform. It soon becomes evident that the rural cantons are remaining faithful to Rome, while Basel, Bern and Schaffhausen side with Zürich.

The pope and the emperor (Clement VII and Charles V) see in this split a chance of containing the Swiss movement for reform. They encourage the rural cantons to band together in 1529 as a Christian Union. Hostilities between the Catholic and Protestant cantons break out in that year and again in 1531. On the second occasion Zwingli himself marches into battle, at Kappel, and loses his life in a decisive Catholic victory.

This disaster ends the pre-eminence of Zürich in the Swiss reformation. But Zwingli's reforms are developed, during the next decades, in a city which has close links with the Swiss federation - Geneva, where Calvin begins preaching in 1536.

Calvin's school of Christ: 1541-1564

John Calvin's first visit to Geneva lasts only two years, to 1538, before he is exiled by a town council alarmed at the rigour of the Christian regime which he wishes to impose on the citizens. He shelters in Strasbourg, until recalled to Geneva in 1541. The town has lapsed in his absence into turmoil and religious discord.

Calvin now sets about creating in Geneva a civic theocracy - a community in which the pastors of the church vigorously supervise moral standards. There have been laws in the medieval church regulating behaviour, often strict but not often effective. Calvin's innovation is to enforce morality in a singularly thorough and joyless manner.

The godly city is run according to the precepts of the Bible. Adultery is punishable by death (Leviticus 20:10). On one occasion a young man is beheaded for striking his parents (Exodus 21:15). The pastors, or ministers, make annual visits to every home to check on morality. Taverns and dancing are banned.

On the credit side, there is a more democratic approach to church affairs. The presbyterian system, introduced by Calvin and seen as a return to early Christian principles, puts power jointly in the hands of pastors and lay elders. Neither group has any authority until elected by the congregation. But once elected, they are empowered to establish a wide-ranging structure of church government.

Council of Trent: 1545-1563

Pope Paul III first proposes in 1536 a council to tackle the issues raised by the Protestant reformers. He also sets up a commission of cardinals to report on abuses within the church. The cardinals find evidence of many of the failings pointed to by Luther, including inadequate training of priests, incompetence of bishops, laxity in the monastic and mendicant orders and the scandal of prelates holding multiple appointments.

It is nine years before Paul III finally assembles his council, at Trent in 1545. The delay is caused by many conflicting interests - including those of the emperor Charles V, who insists on it being held in imperial territory, and Francis I of France who fears it may somehow benefit Charles.

From an unpromising start (only 3 papal legates and 31 prelates at the first session), the council grows in stature during a period of 18 years. There are long intervals during which it is not convened. The sessions occur in 1545-47 under Paul III, in 1551-52 under Julius III and in 1562-63 under Pius IV.

By the end it proves a turning point for the Roman Catholic church, largely because the council responds differently to the two prongs of the Protestant challenge - in each case with considerable vigour.

On the question of abuses within the church, the council accepts the validity of the criticism and puts in place corrective measures - improved seminaries to educate clergy, strict rules about bishops residing in their dioceses, reforms within the monastic orders.

With these practical steps taken, the council refuses by contrast to yield an inch on doctrinal matters. The number of Sacraments remains at seven, marriage for priests is rejected, justification by works as well as by faith is endorsed, and the efficacy of relics and indulgences is reaffirmed - as also is the cult of the Virgin Mary and the saints.

With the ancient colourful certainties thus reinforced, and an improved priesthood entering service (including the invaluable Jesuits), the Roman Catholic church after the Council of Trent is suddenly well placed to confront the Protestant challenge.

During the period of the council, in 1562, the Spanish mystic and ascetic, Teresa of Avila, founds the first of many convents in the movement known as the Carmelite Reform. The same reforming zeal is applied to monasteries by St John of the Cross.

Saints such as Teresa of Avila (and there will be several during the 17th century) are the perfect Roman Catholic response to the Protestant reformers. They are as morally severe as any northern puritan, but there is an ecstatic quality to their religion which is distinctly southern. In its new style, the baroque, the Roman church has the ideal medium in which to hint at religious ecstasy.

It is conventional to call this renewal of Roman Catholicism the Counter-Reformation, but the phrase is too negative. Originally a response to northern reform, the movement amounts in the end to a full-scale southern alternative. Catholic Reformation is a more accurate description.

The English Reformation: 1547-1662

Although Henry VIII severs the church of England from Rome in 1533, religious reform does not begin in earnest until after his death in 1547. Indeed in 1539 parliament passes, at the king's behest, an Act of Six Articles outlawing Lutheran notions such as the marriage of clergy, or any interpretation of the Eucharist differing from that of Rome.

But in the six-year reign of Henry's son, Edward VI, two successive regents of the young king (the dukes of Somerset and Northumberland) press ahead with reform in the Calvinist tradition. This is the time when English cathedrals and churches first have their sculptures and stained-glass windows smashed, and their murals defaced.

On the positive side the period produces two versions of the Prayer Book (1549 and 1552) which are largely the work of Thomas Cranmer. Though modified in some respects in later reigns, Cranmer's superb prose provides the basis of the Book of Common Prayer which becomes accepted from 1662 as the order of service of the church of England.

But the English Reformation has to pass through fire before it is tempered into its final form. In her five-year reign Edward's sister, Mary I, forcibly reimposes Roman Catholicism on England. Protestant martyrs burnt at the stake bequeath to the Anglican church two abiding characteristics - a dislike of religious fervour and a hatred of Roman Catholicism.

During the reign of Mary's sister Elizabeth, whose instinct is for reconciliation after the violent swings of the preceding years, the Calvinists in England become a minority widely referred to as Puritans (because they want to purify the church of all taints of Roman Catholicism).

Among various Puritan sects, the Presbyterians are predominant. In the English Civil War - which can be seen partly as an extension of the struggles of the Reformation - the Presbyterians are the party of parliament. The restoration of the monarchy in 1660 brings back the mainstream of the Anglican church; and from 1662 the mainstream insists upon conformity, even though to a broadly based central position.

The Act of Uniformity of 1662 obliges clergymen in the church of England to assent to the Thirty-Nine Articles. These central tenets of Anglican belief are based on a version drawn up by Cranmer in 1553 and modified ten years later, in Elizabeth's reign, to try and accomodate Catholics who might be willing to give up Rome (and five of the seven Sacraments) and Puritans who might tolerate bishops.

Some 2000 clergy, appointed during the Commonwealth, lose their livings when they reject the Articles in the 1660s. They and their followers become the Nonconformists - a group, much discriminated against, which includes Presbyterians, Congregationalists, Baptists, Quakers and later Methodists.